The present invention relates to a deflecting apparatus for shadow mask color CRT ect. More particularly, it relates to a convergence apparatus for the CRT scanning the display surface by a plurality of electron beams.
Heretofore, in the convergence circuitry of the conventional shadow mask color CRT, the desired correction magnetic field has been produced by feeding a current which is proportional to a parabolic waveform voltage given by integrating the horizontal deflecting current or the vertical deflecting current, to a horizontal or vertical convergence coil.
However, in the conventional apparatus, a uniform correction could not be attained on all of the picture surface of the CRT. Especially, at the four corners of the picture surface, the divergence is large. The convergence corrections needed at zones on the CRT picture surface are affected by the fluctuations of the CRT itself and the deflecting coil etc.. Accordingly, it has been difficult to attain convergence of the beam having high accuracy on all of the picture surface of the CRT.